The long-range goal of the proposed studies is to identify mechanisms of cell fate specification and movement during vertebrate development. The focus is on the Nodal TGF pathway, which plays fundamental roles in mesendoderm specification and left-right axis determination, and the Toddler GPCR signaling pathway, which is essential for normal internalization of mesendoderm during gastrulation. The essential functions of Nodal and Toddler signaling are firmly established but the mechanisms by which they exert their roles are largely elusive to gain a deeper understanding of Nodal morphogen signaling, this project will determine how feedback inhibition regulates mesendoderm formation and how graded Nodal signaling is interpreted in responding cells. To reveal the cellular and molecular roles of Toddler signaling, this project will determine how Toddler signaling regulates the movement and adhesion of cells. These studies will be performed in zebrafish embryos, because sophisticated live imaging can be combined with genetic and genomic approaches. The proposed studies will provide general insights into how signals pattern fields of cells and control the movement of cells. Since Nodal and Toddler signaling are conserved in humans, the proposed studies will also provide the context necessary to understand birth defects, cancer and other diseases and to inform strategies to program cells to form specific cell types and tissues for disease-modeling and regeneration.